Miniature interference spectrometer and measurement method thereof

Abstract

The present invention provides a miniature interference spectrometer and a measurement method thereof. The spectrometer comprises a light source system, a phase modulation system, a digital micromirror array, and a detector system. The light source system is used to emit a parallel light beam, which, after distributed phase modulation by the phase modulation system, produces a light field array composed of N×N light field units. The digital micromirror array is used to select the light field array so that at least two light field units are incident on the detector system, causing interference, thereby obtaining an interference pattern signal and acquiring spectral information of the parallel light beam. The present invention avoids the high-precision manufacturing and control issues of moving mirror scanning in traditional Fourier transform spectrometers. By using a driving voltage to switch the digital micromirror units of the digital micromirror array on and off, the system eliminates the need for a beam splitting system, reduces the system's volume and weight, and improves its energy efficiency.

Description

Technical Field

[0001] The present invention relates to the field of spectral technology, and in particular to a miniature interference spectrometer and a measurement method thereof. Background Art

[0002] Spectroscopic technology can obtain information about the composition and content of target substances. It has been increasingly applied in fields such as physical experiments, chemical analysis, biological characterization, medical testing, and ecological and environmental protection, and has played a vital role in the exploration and discovery of new materials, new energy sources, and the unknown world. To obtain the spectral characteristics of the target, the detected complex light must be spectrally decomposed. Currently, commonly used spectroscopic instruments mainly use filter spectroscopy, prism spectroscopy, grating spectroscopy, and interference spectroscopy. Among them, Fourier transform spectroscopy, which uses interference spectroscopy, has become a high-end instrument in many application fields due to its advantages such as multi-channel, high throughput, accurate wavenumber, and low stray light.

[0003] In recent years, with the emergence and development of emerging scientific and technological fields such as space exploration, aerial remote sensing, Earth surveying, atmospheric monitoring, and military reconnaissance, the specialized applications and environments of these instruments have created an urgent need for miniaturized, static Fourier transform spectrometers. This escalating demand has led to insurmountable technical bottlenecks in conventional Fourier transform spectrometers. Currently, the Fourier transform spectrometers commonly used in laboratories employ a time-modulated interferometer structure, where a moving mirror scans the interferometer to generate an optical path difference to obtain spectral information. These instruments incorporate a high-precision moving mirror scanning mechanism for precise sampling of the interferogram. This mechanism is complex to manufacture, sensitive to vibration, and demanding in its operating environment. Furthermore, the moving mirror scanning mechanism is large and heavy. Furthermore, the use of a beam splitter for light separation results in half the energy loss, reducing system stability and reliability, making it unsuitable for aerospace applications such as meteorological observation and atmospheric remote sensing. This, in turn, limits its application in high-tech fields such as space exploration, meteorological remote sensing, and military reconnaissance. Summary of the Invention

[0004] In light of the above issues, the present invention proposes a miniature interference spectrometer and its measurement method. Using two stepped micromirrors and a digital micromirror, spatial phase modulation of the lateral light field is combined with gated interference of the light field unit to obtain the interference pattern signal of each sampled optical path difference. This eliminates the moving mirror scanning mechanism and beam splitting system of a traditional Fourier transform spectrometer, reduces the system's volume and weight, and improves energy efficiency. The proposed miniature spectrometer structure is characterized by its miniaturization, lightweight, and high energy efficiency.

[0005] To achieve the above objectives, the present invention adopts the following specific technical solutions:

[0006] The present invention provides a miniature interference spectrometer, comprising: a light source system, a phase modulation system, a digital micromirror array and a detector system;

[0007] The light source system is used to emit a parallel light beam, which is then subjected to distributed phase modulation by the phase modulation system to obtain a light field array consisting of N×N light field units. The digital micromirror array is used to select the light field array so that at least two light field units are incident on the detector system to interfere with each other, thereby obtaining an interference pattern signal and acquiring the spectral information of the parallel light beam.

[0008] Preferably, the light source system includes: a light source and a collimator; the light source is used to emit a divergent light beam, which is collimated by the collimator to form a parallel light beam and is incident on the phase modulation system.

[0009] Preferably, the phase modulation system comprises: a longitudinal step micromirror and a transverse step micromirror;

[0010] The parallel light beam passes through the longitudinal step micromirror and the transverse step micromirror in sequence to form a light field array composed of N×N light field units, which is incident on the digital micromirror array.

[0011] Preferably, the longitudinal step micromirror is composed of N column step units whose step directions are perpendicular to the horizontal plane; the direction of the column step units is perpendicular to the horizontal plane;

[0012] The optical path delay generated when the parallel light beam propagates in the i-th column step unit along the horizontal direction is: δ1(i)=i(n-1)d;

[0013] Wherein, i=0, 1, 2, ..., N-1; n is the refractive index of the longitudinal step micromirror material; d is the height of the column step unit, and N is the number of column step units.

[0014] Preferably, the transverse step micromirror is composed of N row step units whose step directions are parallel to the horizontal plane; the directions of the row step units are all parallel to the horizontal plane;

[0015] The optical path delay generated when the parallel light beam propagates in the jth row step unit along the vertical direction is: δ2(j)=j(n-1)h;

[0016] Wherein, j=0, 1, 2, ..., N-1; n is the refractive index of the material of the lateral step micromirror; h is the height of the row step unit, and N is the number of the row step unit.

[0017] Preferably, the step unit heights of the transverse step micromirror and the longitudinal step micromirror satisfy the following relationship:

[0018]

[0019] Among them, λ minis the minimum wavelength in a parallel beam of light.

[0020] Preferably, the digital micromirror array consists of N×N digital micromirror units;

[0021] The process of gating the light field array by the digital micromirror array is as follows: by controlling the driving voltage of the digital micromirror array, and then controlling the rotation angle of the digital micromirror unit, at the same time, the two light beams of the light field units in the light field array corresponding to the digital micromirror unit (0,0) and the digital micromirror unit (i,j) are incident on the detector system, where i and j are not 0 at the same time.

[0022] Preferably, the two light beams selected by the digital micromirror array have a preset optical path difference, and the two light beams with linearly increasing optical path differences are sequentially selected by controlling the digital micromirror array to be incident on the detector system.

[0023] Preferably, the detector system comprises: a focusing mirror and a photodetector;

[0024] The two beams selected by the digital micromirror array are converged by the focusing mirror and then incident on the photodetector to cause interference;

[0025] defining two light beams gated by the digital micromirror array as a group of light beams;

[0026] When the digital micromirror array selects a first group of light beams having a first preset optical path difference, a first group of interference pattern signals is obtained;

[0027] When the digital micromirror array selects a second group of light beams having a second preset optical path difference, a second group of interference pattern signals is obtained;

[0028] When all interference pattern signals are obtained, the spectrum information of the parallel light beam is obtained by performing discrete Fourier transform on all interference pattern signals.

[0029] The present invention also provides a measurement method of a micro interference spectrometer, comprising the following steps:

[0030] S1, the light source emits a parallel beam incident on the phase modulation system;

[0031] S2, the parallel light beam passes through the longitudinal step micromirror and the transverse step micromirror in the phase modulation system in sequence and becomes a light field array composed of N×N light field units, which is incident on the digital micromirror array;

[0032] S3, controlling the N×N digital micromirror units of the digital micromirror array to achieve gating of different light field units in the light field array;

[0033] S4. After the light beams corresponding to at least two light field units with a preset optical path difference selected by the digital micromirror array enter the detector system and interfere with each other, an interference pattern signal is obtained, thereby obtaining spectral information of the parallel light beams.

[0034] Compared to existing technologies, this method uses two stepped micromirrors to perform aperture segmentation and distributed phase modulation on the incident light field, generating spatially distributed phase delays. A digital micromirror array then performs gated interferometry on each light field unit to obtain an interferogram signal with a specific optical path difference. This avoids the high-precision manufacturing and control issues associated with moving mirror scanning in traditional Fourier transform spectrometers. By using a driving voltage to switch the individual micromirror units of the digital micromirror array on and off, the system eliminates the need for a beam splitting system, reduces its size and weight, and improves its energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the structure of a micro-interference spectrometer provided according to an embodiment of the present invention.

[0036] Figure 2 Schematic diagram of the structure of the longitudinal stepped micromirror in the micro interference spectrometer provided according to an embodiment of the present invention.

[0037] Figure 3 Schematic diagram of the structure of a lateral stepped micromirror in a micro interference spectrometer provided according to an embodiment of the present invention.

[0038] Figure 4 4 is a flow chart of a micro-interference spectrometer measurement method provided according to an embodiment of the present invention.

[0039] Figure 5 It is a flowchart of a micro-interference spectrometer measurement method provided according to an embodiment of the present invention.

[0040] The reference numerals include: light source 1 , collimating mirror 2 , longitudinal step micromirror 3 , transverse step micromirror 4 , digital micromirror array 5 , focusing mirror 6 and photodetector 7 . DETAILED DESCRIPTION

[0041] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, identical modules are denoted by identical reference numerals. In the case of identical reference numerals, their names and functions are also identical. Therefore, their detailed description will not be repeated.

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0043] Figure 1The structure of a micro-interference spectrometer provided according to an embodiment of the present invention is shown.

[0044] like Figure 1 As shown, the micro-interference spectrometer provided by the embodiment of the present invention includes: a light source system, a phase modulation system, a digital micromirror array 5 and a detector system.

[0045] The light source system includes: a light source 1 and a collimator 2; the light source 1 emits a divergent light beam with a certain spectral radiation range, which is collimated by the collimator 2 to form a parallel light beam and is incident on the phase modulation system.

[0046] The phase modulation system includes a longitudinal step micromirror 3 and a transverse step micromirror 4 .

[0047] The parallel light beam is transmitted through the longitudinal step micromirror 3 and the transverse step micromirror 4 in sequence to form a light field array consisting of N×N light field units and is incident on the digital micromirror array 5 .

[0048] Figure 2 The structure of the longitudinal stepped micromirror in the micro interference spectrometer provided according to an embodiment of the present invention is shown.

[0049] like Figure 2 As shown, the longitudinal step micromirror 3 is used to perform distributed phase modulation on the parallel light beam in the horizontal direction;

[0050] The longitudinal step micromirror 3 is composed of N columns of step units with the step direction perpendicular to the horizontal plane. Assume that the number of step units of the longitudinal step micromirror 3 is N, the step unit width is a, the step unit height is d, and the step unit direction is perpendicular to the horizontal plane.

[0051] For the longitudinal step micromirror 3, a parallel light beam propagates through it. When propagating through different columns of step elements, the parallel light beam travels different optical paths. Light beams transmitted between adjacent columns of step elements experience a specific optical path delay (n-1)d, where n is the refractive index of the material of the longitudinal step micromirror 3. Therefore, the optical path delay incurred by light propagating through the i-th (i=0, 1, 2, ..., N-1)th column of step elements along the horizontal direction is δ1(i)=i(n-1)d.

[0052] Figure 3 The structure of a lateral stepped micromirror in a micro interference spectrometer provided according to an embodiment of the present invention is shown.

[0053] like Figure 3 As shown, the transverse stepped micromirror 4 is used to perform distributed phase modulation on the parallel light beam in the vertical direction.

[0054] The lateral step micromirror 4 is composed of N rows of step units with their step directions parallel to the horizontal plane. Assume that the number of step units of the lateral step micromirror 4 is N, the step unit width is b, the step unit height is h, and the step unit directions are all parallel to the horizontal plane.

[0055] For the transverse step micromirror 4, a parallel light beam propagates through it. This light beam travels through different optical paths as it propagates through different rows of step elements. The transmitted light between adjacent rows of step elements experiences a specific optical path delay (n-1)h, where n is the refractive index of the transverse step micromirror material. Therefore, the optical path delay incurred by light propagating through the jth (j = 0, 1, 2, ..., N-1) row of step elements along the vertical direction is δ2(j) = j(n-1)h.

[0056] The step unit directions of the transverse step micromirror 4 and the longitudinal step micromirror 3 are orthogonal in the transverse space, thereby dividing the light field of the parallel light beam into N×N light field units in the transverse space, and each light field unit corresponds to a specific row step unit of the transverse step micromirror 4 and a specific column step unit of the longitudinal step micromirror 3.

[0057] The light field array composed of N×N light field units formed after being transmitted through the transverse stepped micromirror 4 is incident on the digital micromirror array 5 .

[0058] The digital micromirror array 5 is composed of N×N digital micromirror units, each of which corresponds to a specific light field unit formed by the row step units of the transverse step micromirror 4 and the column step units of the longitudinal step micromirror 3 .

[0059] The digital micromirror array 5 can be placed perpendicular to the optical axis of the parallel light beam or tilted at a certain angle. Each digital micromirror unit of the digital micromirror array 5 can be rotated at a certain angle along its rotation axis to achieve gating interference on any spatial light field unit.

[0060] The digital micromirror unit corresponding to the light field unit reflected by the i-th row step unit of the transverse step micromirror 3 and the j-th column step unit of the longitudinal step micromirror 4 is turned on, that is, the digital micromirror unit (i, j) = (0, 0) is turned on, while the remaining digital micromirror units are kept in the off state.

[0061] Then, the remaining digital micromirror units are turned on in a row-by-row and column-by-column direction, and only one digital micromirror unit other than (i, j) = (0, 0) is kept in the turned-on state at each moment.

[0062] At the same time, only two beams from different light field units are incident on the detector system and interfere with each other.

[0063] The detector system includes: a focusing lens 6 and a photoelectric detector 7; the photoelectric detector 7 is a point detector.

[0064] After the two light beams from different light field units are converged by the focusing mirror 6, they are incident on the photodetector 7 and interfere with each other to obtain an interference pattern signal, thereby obtaining the spectral information of the parallel light beams.

[0065] When the (i, j)th light field unit interferes with the (0, 0)th light field unit, the optical path difference between the two coherent light beams is:

[0066] δ(i,j)=δ1(i)+δ2(j)-δ1(0)-δ2(0)=(n-1)(jh+id)

[0067] Therefore, the intensity of the (i, j)th interference pattern signal is:

[0068]

[0069] By performing discrete Fourier transform demodulation on the interference pattern sequence, the spectral information of the parallel light beam can be restored.

[0070] In order to form a continuous optical path difference sequence, the transverse step micromirror 4 and the longitudinal step micromirror 3 must achieve mutual optical path compensation. Optical path complementarity can be achieved by matching the step unit heights of the transverse step micromirror 4 and the longitudinal step micromirror 3, so that the step unit height of the transverse step micromirror 4 is N times the step unit height of the longitudinal step micromirror 3, that is, h = Nd.

[0071] When the height relationship between the horizontal step micromirror 4 and the vertical step micromirror 3 is h=Nd, the optical path difference sampling array is:

[0072] δ(i,j)=(n-1)(jh+id)=(n-1)(jN+i)d

[0073] In order to avoid spectral aliasing during the spectrum restoration process, the optical path difference sampling interval must be less than or equal to twice the minimum wavelength of the optical signal, that is:

[0074]

[0075] Therefore, the height of the step unit of the lateral step micromirror 4 and the longitudinal step micromirror 3 must satisfy the following relationship:

[0076]

[0077] At this point, the restored spectrum is in the form of:

[0078]

[0079] Where ν is the wave number of the interference light signal. For light with a wavelength of λ, ν = 1 / λ.

[0080] According to the discrete Fourier transform theory, the spectral resolution of the system is:

[0081] Figure 4 A schematic flow chart of a micro-interference spectrometer measurement method according to an embodiment of the present invention is shown.

[0082] Figure 5 A flowchart of a micro-interference spectrometer measurement method according to an embodiment of the present invention is shown.

[0083] like Figure 4 and Figure 5 As shown, the micro-interference spectrometer measurement method provided by the embodiment of the present invention includes the following steps:

[0084] S1. The light source emits a parallel beam of light that is incident on the phase modulation system.

[0085] Fix the collimator mirror on the platform base; use a divergent laser with a wavelength within the spectrum as the incident light, place the laser source at the front focal plane of the collimator mirror to ensure that the outgoing light is parallel; replace the laser light source with a broadband light source.

[0086] S2. The parallel light beam passes through the longitudinal step micromirror and the transverse step micromirror in the phase modulation system in sequence and becomes a light field array composed of N×N light field units, which is incident on the digital micromirror array.

[0087] Place the longitudinal step micromirror in the outgoing light path of the collimator and align the center;

[0088] The transverse step micromirror is placed in the outgoing light path of the longitudinal step micromirror and the center is aligned; the direction of the transverse step micromirror is adjusted so that the step directions of the transverse step micromirror and the longitudinal step micromirror are perpendicular to each other.

[0089] S3. By controlling the N×N digital micromirror units of the digital micromirror array, gating different light field units in the light field array is achieved.

[0090] The digital micromirror array is placed in the transmission light path of the lateral step micromirror and is centrally aligned;

[0091] By adjusting the angle of the digital micromirror array, the digital micromirror units are made to correspond one to one with the surfaces of each step unit of the longitudinal step micromirror and the transverse step micromirror;

[0092] The focusing mirror is placed in the output light path of the digital micromirror; the single point detector is placed at the focal plane of the focusing mirror;

[0093] Adjusting the driving voltage of the digital micromirror so that it can gate any two light field units in the spatial light field array;

[0094] S4. After the light beams corresponding to at least two light field units with a preset optical path difference selected by the digital micromirror array enter the detector system and interfere with each other, an interference pattern signal is obtained, thereby obtaining spectral information of the parallel light beams.

[0095] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0096] The above specific embodiments of the present invention do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A miniature interference spectrometer, characterized in that: include: Light source system, phase modulation system, digital micromirror array and detector system; The light source system is used to emit a parallel light beam, which is subjected to distributed phase modulation by the phase modulation system to obtain a light field array composed of N×N light field units; the digital micromirror array is used to gate the light field array so that two of the light field units are incident on the detector system to cause interference, thereby obtaining an interference pattern signal and acquiring spectral information of the parallel light beam; The phase modulation system includes: a longitudinal step micromirror and a transverse step micromirror; the parallel light beam passes through the longitudinal step micromirror and the transverse step micromirror in sequence to form a light field array consisting of N×N light field units, which is incident on the digital micromirror array; The longitudinal step micromirror is composed of N column step units whose step directions are perpendicular to the horizontal plane; the direction of the column step units is perpendicular to the horizontal plane; The optical path delay generated when the parallel light beam is transmitted in the i-th column step unit along the horizontal direction is: ; Where i=0,1,2,…,N-1; n is the refractive index of the longitudinal step micromirror material; d is the height of the column step unit, and N is the number of the column step unit; The transverse step micromirror is composed of N row step units whose step directions are parallel to the horizontal plane; the directions of the row step units are all parallel to the horizontal plane; The optical path delay generated when the parallel light beam is transmitted in the j-th row step unit along the vertical direction is: ; Where j = 0, 1, 2, ..., N-1; n is the refractive index of the material of the transverse step micromirror; h is the height of the row step unit, and N is the number of the row step unit; The step unit heights of the transverse step micromirror and the longitudinal step micromirror satisfy the following relationship: ， Among them, λ min is the minimum wavelength in the parallel light beam; The digital micromirror array consists of N×N digital micromirror units; The process of gating the light field array by the digital micromirror array is as follows: controlling the driving voltage of the digital micromirror array and thereby controlling the rotation angle of the digital micromirror unit so that at the same time, two light beams of the light field units in the light field array corresponding to the digital micromirror unit (0, 0) and the digital micromirror unit (i, j) are incident on the detector system, wherein i and j are not 0 at the same time; The two light beams selected by the digital micromirror array have a preset optical path difference, and the two light beams with linearly increasing optical path differences are sequentially selected by controlling the digital micromirror array to be incident on the detector system.

2. The micro-interference spectrometer according to claim 1, characterized in that The light source system includes: a light source and a collimator; the light source is used to emit a divergent light beam, and the divergent light beam is collimated by the collimator to form a parallel light beam, which is incident on the phase modulation system.

3. The micro-interference spectrometer according to claim 1, characterized in that: The detector system includes: a focusing mirror and a photoelectric detector; The two light beams selected by the digital micromirror array are converged by the focusing mirror and incident on the photodetector to cause interference; defining two light beams selected by the digital micromirror array as a group of light beams; When the digital micromirror array selects a first group of light beams having a first preset optical path difference, a first group of interference pattern signals is obtained; When the digital micromirror array selects a second group of light beams having a second preset optical path difference, a second group of interference pattern signals is obtained; When all interference pattern signals are obtained, spectrum information of the parallel light beam is obtained by performing discrete Fourier transform on all the interference pattern signals.

4. A measurement method of a micro-interference spectrometer according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, the light source emits a parallel beam incident on the phase modulation system; S2, the parallel light beam passes through the longitudinal step micromirror and the transverse step micromirror in the phase modulation system in sequence and becomes a light field array composed of N×N light field units, which is incident on the digital micromirror array; S3, controlling the N×N digital micromirror units of the digital micromirror array to achieve gating of different light field units in the light field array; S4. After the light beams corresponding to at least two light field units with a preset optical path difference selected by the digital micromirror array enter the detector system and interfere with each other, an interference pattern signal is obtained, thereby obtaining spectral information of the parallel light beams.

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